Computer numerical controlled (CNC) machine tools allow machinists to repeat a machining process on multiple work pieces with high accuracy. A controller operates the machine tool and positions the work piece in accordance with a sequence of programmed instructions. The accuracy of the machining process, and correspondingly the quality of the finished work piece, relies on the controller having accurate data on the positions of the components of the machine tool and the work piece during the machining process.
Rotary position encoders are used in CNC machine tools to detect the rotational position of a rotatable shaft, such as the shaft of an electric motor. The environment in which CNC machine tools typically operate presents several challenges to conventional rotary position encoders. For example, waste material removed from the work piece and lubricant used during the machining process may contaminate and cause premature failure of the detector used to determine the rotational position of the shaft or the mechanism used to connect the encoder to the shaft. Additionally, the mechanical designs of conventional rotary position encoders are either susceptible to failure due to the vibrations and other forces experienced by the encoder during machining processes or are overly expensive and complex.